Historically, research on genetic and environmental factors affecting reproduction and subsequent development of the offspring has been centered on the female. Only recently have we come to appreciate the extent and complexity of the role that the male may play. In animals, there is substantial body of experimental evidence indicating that treatment of males with toxicant, followed by mating to untreated females, can result in a variety of adverse reproductive outcomes. These adverse effects on offspring cannot necessarily be predicted by the usual tests of male reproductive function, for these may be normal while the offspring are malformed or die. Only a handful of studies have addressed paternally mediated adverse reproductive outcomes in humans. These are typically marked by inadequate data, narrow exposure focus, and methodologic problems. During this year we have surveyed the world literature, both animal and human, to determine the advisability and feasibility of conducting a broader and more rigorous study of male-mediated reproductive outcomes in humans. This has provided a comprehensive review and synthesis of the literature that is about to be submitted for publication; an invited presentation of the findings was given at the first professional meeting to be devoted to male-mediated reproductive effects. Based on this work, the need for an epidemiologic study of male-mediated reproductive outcomes was clear. We searched for an appropriate data set that would serve at the basis for such a study, and found it at the University of Bristol, England. We have determined the design and scope of this investigation and moved to secure the data that will be available early in 1993. Work on occupational and environmental hazard classifications is proceeding, and analysis will be underway as soon as the data tapes are secured.